Australasian Science: Australia's authority on science since 1938

Kangaroo Teeth Tell Their Story of Evolution

By John Long

An analysis of kangaroo teeth reveals a rapid burst of evolution in response to the expansion of grassland rather than drier climate conditions.

Kangaroos and wallabies are iconic Australian macropods with a reasonably good fossil record extending back at least 25 million years. The oldest kangaroos include small hopping forms like Ngamaroo archeri from the Lake Eyre Basin of South Australia. While it is clear that the group radiated into many lineages in the Miocene (23–25 million years) it has been unclear when the modern macropod fauna evolved and what environmental drivers directed their radiation.

A landmark paper published in Science in October (https://goo.gl/jUUB3f) has now demonstrated that modern kangaroos and some recently extinct short-faced forms called sthenurines underwent a rapid burst of evolution in the Pliocene 5–2.6 million years ago. The research by former PhD student Aidan Couzens and Gavin Prideaux, both of Flinders University, followed a new approach to the problem of how modern kangaroos evolved by looking at the teeth of living and fossil kangaroos.

Plant-eaters that eat a lot of grasses suffer increased dental abrasion due to the high silica content and adhering dust. The evolutionary response to this by kangaroos was to make the teeth taller, or higher-crowned, increasing the durability of their teeth.

Kangaroos also responded to the aridification in a slightly different way than the herbivores living in the northern hemisphere. Unlike horses, whose teeth continually developed higher crowns to cope with increased grazing on grasses over a long period of time (horse evolution spans some 60 million years), kangaroos dealt with the initial onset of aridification in the Miocene by getting larger. However, the major burst of diversification within the group is tied not to drying conditions but to the relatively short greenhouse climatic interval of the early Pliocene 5–3.5 million years ago, when forested habitats became more widespread.

Among the macropods that first appeared during the early Pliocene was the ancestor of today’s iconic red and grey kangaroos. But only after the greenhouse phase ended and grasslands spread across an increasingly arid Australia did this group radiate into specialist grass-eating niches. This occurred several million years later than the equivalent transition among Northern Hemisphere herbivores.

Mammal evolution expert, Prof David Polly of Indiana University, said: “One of the most interesting things that they found was that kangaroos changed with the grass, not with the rainfall. Often tooth structure in the fossil record appears to be directly linked to aridity, but several recent lines of evidence suggest it isn’t that simple. Couzens and Prideaux help confirm why by showing that kangaroo teeth follow the abrasive diet associated with spread of grassland, which in Australia happens to be partially decoupled from the global aridification.”

The new study also highlights the value of palaeontology in discovering the underlying narratives about our iconic animals, about how they can survive in modern Australia’s harsh desert areas and surrounding low nutrient sparse lands. We should regard kangaroos in a new light. They are supreme adaptors that can serve as an inspiration to our nation through what they have endured and become, not just because they appear cute and cuddly in our wildlife enclosures.


John Long is Strategic Professor in Palaeontology at Flinders University, and is Past President of the Society of Vertebrate Paleontology.